1. Field of the Invention
The present invention relates to an optical scanning device for scanning the surface of a scanning member such as a photosensitive member or the like with an optical beam emitted from a light source. More specifically, the present invention relates to an optical scanning device provided with a casing having an assembly of optical members such as light source, mirror, lenses and the like.
2. Background of the Invention
Conventional optical scanning devices write image data on the surface of a photosensitive member by exposing the surface of said photosensitive member via an optical beam emitted from a light source and scanning the surface of the photosensitive member via an optical beam. Conventional optical scanning devices have optical members such as a light source for emitting an optical beam, rotatable polygonal mirror for reflecting said optical beam emitted by the light source, lens for projecting said reflected optical beam, mirrors for reflecting the optical beam that has passed through said lens toward the surface of a photosensitive member and like elements, all of which are accommodated within a casing. The aforesaid casing comprises a concave shaped optical box accommodating the mounted optical members and a cover fitted on the top of said optical box. The photosensitive member arranged beneath the aforesaid casing. Accordingly, an aperture must be provided in the optical box of the casing to emit the optical beam from the casing in order to expose the surface of the photosensitive member via the optical beam reflected by the mirror toward the surface of said photosensitive member.
The lengthwise orientation of the aforesaid aperture must coincide with the length of the optical beam main scanning direction, i.e., the axial direction of the photosensitive member, in order that the optical beam emitted through said aperture may scan the surface of the photosensitive member to write the image data thereon. The aperture must have a length substantially similar to the length of the photosensitive member in the axial direction and be positioned in near proximity to said photosensitive member. When the aperture has a length of the aforesaid substantially similar dimension and is formed in optical box wherein are mounted the optical members, said optical box is readily subject to distortions such that the relative positioning of the optical members mounted in said optical box cannot be uniformly maintained. Furthermore, when the relative positioning of the aforesaid optical members changes, the optical path of the emitted beam is subject to dislocation so as to preclude high-precision scanning via said optical beam.
Optical scanning devices have also been provided with a casing comprising an optical box having a cover disposed at the bottom side thereof, with said optical box being positioned on the top of said casing. In this arrangement, an aperture is not formed on said optical box accommodating the mounted optical members therein but rather said aperture is provided on the cover of said optical box, such that the cover is readily subject to distortion due to the aperture provided on said cover and further adversely affecting the relative positional relationships of the optical members. The mounting plane of the optical members of the optical box is essentially flat, i.e., said plane occupies the majority of the surface area of the casing, such that when, for example, a force is added in the direction of a distortion produced by a temperature rise within the apparatus via heat generated from the optical members within the casing, the relative positional relationships of the optical members within said casing changes causing a dislocation in the optical path of the beam so as to preclude high-precision scanning via said optical beam.